Electronic transmission device, and signal transmission method

ABSTRACT

An electronic signal transmission apparatus executes an authentication process with a transmitting electronic device over a transmission line and receives an encrypted signal and first and second key information therefrom. The encrypted signal is decrypted based on the first key information, displayed and/or recorded, and re-encrypted using the second key information. The encrypted signal is transmitted to another electronic transmission apparatus if that apparatus does not have a recording capability and determined to be authorized using a second authentication process. The re-encrypted signal is sent to the another electronic transmission apparatus if that device has a recording capability and is authorized.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/044,422, filed Jan. 11, 2002, which claims priority from JapanesePriority Document No. 2001-008249, filed on Jan. 16, 2001 with theJapanese Patent Office, the disclosures of which are hereby incorporatedby reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electronic transmission device and a signaltransmission method using such electronic transmission device. Moreparticularly, the present invention relates to an electronictransmission device that can avoid signal delay when connected in serialform to another electronic device even an authentication process isapplied at each of the electronic transmission device.

2. Description of the Related Art

Conventionally in a computer apparatus or the like, a digital imagesignal is once converted into an analog image signal and then suppliedto a display device by way of an analog transmission line. However, as adisplay device such as a LCD (Liquid Crystal Display) that is driven itsdisplay section by the digital signal is getting popular, a digitaltransmission method for driving the display device without convertingthe digital image signal into the analog image signal has becomestandard in order to avoid deterioration of image quality and reductionof cost.

FIG. 6 shows a construction chart of a digital connection, wherein twoelectronic devices such as a signal transmission device 100 and a signalreception device 130 are connected by way of a digital transmissionline. Regarding the digital transmission line, the DVI (Digital VisualInterface) format is proposed by the DDWG (Digital Display WorkingGroup), for example. In this DVI format, digitized three primary colorimage signals are serially transmitted color by color at base bandtransmission through the TMDS (Transition Minimized DifferentialSignals) high-speed transmission line developed by I²C Silicon Image Co.Further, a two-way transmission line such as the I²C (Inter IntegratedCircuit) bus having a lower transmission speed than the TMDS high-speedtransmission line (here-in after referred to as a high-speed serial bus)is provided, and this two-way transmission line (here-in after referredto as a two-way serial bus) is applied as a transmission line for theDDC (Display Data Channel) format in relating to the Plug & Playproposed by the VESA (Video Electronics Standards Association).

A transmission band for this high-speed serial bus of the DVI format cantransmit image signal by using 3 channels (single-link) high-speedserial bus, as shown in FIG. 7, in a case when data amount oftransmitting image signal is up to about 165 M-pixels/sec., namely animage display of a SXGA (Super Extended Graphics Array) (1280pixels×1024 pixels) size and a vertical frequency of 85 Hz with a GTF(General Timing Formula) blanking is executed or an image display of anUXGA (ultra Extended Graphics Array) (1600 pixels×1200 pixels) size anda vertical frequency of 60 Hz with a GTF blanking is executed. Howeverin a case when an image display of an UXGA (1600 pixels×1200 pixels)size and a vertical frequency of 75 Hz with a GTF blanking is executed,a 2-link high-speed serial bus is employed.

Contents data transmitted through such digital transmission line likethe above-described can be easily and infinitely copied in a perfectform because of the digital signal transmission. This becomes a greatmerit for a user, but becomes serious problems for a provider whosupplies copyrighted materials such as films with a legal protection.Because of this, it is proposed that in case of transmitting a digitalsignal of the contents data through the digital transmission line of theDVI format, an encryption for the copyright protection is executed and adecryption is made possible at a receiving side only if anauthentication is properly conducted.

By the way, between two electronic device for legal protection, namelyan authentication process is executed between a signal transmissiondevice for outputting encrypted digital image signal of the contents anda signal reception device for receiving the signal from the signaltransmission device as a pair, and if it is judged that an authorizeddevice is connected, then key information for decrypting the encrypteddigital image signal of the contents data is supplied. In this case,image display operations by the plural signal reception devices areexecuted in order to improve advertising effect, such plural signalreception devices are connected to multi-stage by a star connection asshown in FIG. 8. In this case, when the authentication is properlyexecuted with the signal transmission device 100 and each of the signalreception devices 130, the key information is supplied to the signalreception device from the signal transmission device and it becomespossible to execute the image display by the signal reception device towhich the key information is supplied.

If a relay function is added to the signal reception device, a pluralityof signal reception devices 130 are connected to the signal transmissiondevice 100 in a multistage daisy-chain connection as shown in FIG. 9.

FIG. 10 shows a conventional signal reception device to which a relayfunction is employed. A signal receiving section 132 of a signalreception device 130 is connected to a device of a signal transmittingside through a high-speed serial bus connected to a connector 131, and asignal transmitting/receiving section 133 is connected to a signaltransmitting side through a two-way serial bus connected to theconnector 131. Further a transmitting section 142 is also connected tothe signal receiving side through the high-speed serial bus connected tothe connector 141 and the signal transmitting/receiving section 143 isalso connected to the signal receiving side through the two-way serialbus connected to the connector 141.

A decrypting section 151 is connected to the signal receiving section132 and supplies an encrypted digital signal DGs transmitted from thesignal transmitting side to a decrypting section 151. Further the signaltransmitting/receiving sections 133, 143 are connected to anauthentication process section 150 and executes an authenticationprocess together with the signal transmitting side and the signalreceiving side by way of the two-way serial bus.

In case of transmitting the encrypted digital image signal of thecontents data for a legal protection, the authentication process isexecuted between the authentication process section 150 of the signalreception device and the signal transmitting side, and when keyinformation Ka is supplied from the signal transmitting side to theauthentication process section 150 and when authenticated as aconnection of an authorized device, the authentication process section150 supplies the key information Ka to the decrypting section 151.

The decrypting section 151 executes the decryption of the encrypteddigital signal DGs supplied from the signal receiving section 132 byapplying the key information Ka supplied from the authentication processsection 150. The decryption is executed at the decrypting section 151,and thus obtained three primary color digital image signals DG aresupplied to a display section 152 and image display is executed at thedisplay section 152. Further the three primary color digital imagesignals DG obtained at the decrypting section 151 are also supplied toan encryption section 155.

When the relay for the digital image signal of the contents data isexecuted, key information is supplied from the authentication processsection 150 to the encryption section 155 and an encryption of the threeprimary color digital image signals DG is executed by applying the keyinformation supplied from the authentication process section 150 in theencryption section 155. A digital signal DGt generated at the encryptionsection 155 is supplied to the transmitting section 142, and is thensupplied to the signal receiving side from the transmitting section 142through the high-speed serial bus and the connector 141.

Further, in the authentication process section 150, the authenticationprocess is executed with the signal receiving side connected to theconnector 141, and if the authentication process indicates that thedevice is the authorized one, key information Kb for decrypting theencrypted digital signal DGt is also supplied to the signal receivingside.

Thus the image display is done by decrypting the received digital imagesignal DGs and further thus obtained digital signal is supplied toanother signal receiving side by re-encrypting the decrypted signal DG.In this case, when it is judged by the authentication process with thesignal receiving side that the authorized device is connected, then thekey information Kb for decrypting the supplied digital image signal istransmitted to the signal receiving side. Accordingly, when a pluralityof devices is connected in daisy-chain connection, it is possible toattain the legal protection properly.

In this case, when a plurality of signal reception devices is connectedto a single signal transmission device as shown in FIG. 8, due tolimitation of size and design of the signal transmission device, thenumber of connectors to be provided on the signal transmission devicehas a limitation, and there is a case where desired numbers of signalreception devices cannot be connected.

The encrypted signal is executed the image display after decryption andthus decrypted signal is supplied to another signal reception deviceafter re-encrypting the decrypted signal as shown in FIG. 10, then thedecryption and encryption process are to be done at every time when thesignal is relayed. Accordingly, the digital image signal of the contentsdata is delayed at every time when relayed through one signal receptiondevice by the decryption and encryption process, so that if relativelylarge number of signal reception devices are connected in thedaisy-chain connection, the time delay is accumulated at the lastconnected signal reception device. In this case, the time difference ofthe displayed image between the display image by the signal receptiondevice of the signal transmission device side and the display image bythe signal reception device connected at the end of the daisy-chainconnection becomes relatively large and thereby, the simultaneity of theimage display cannot be maintained.

SUMMARY OF THE INVENTION

According to the present invention, a signal transmission method capableof transmitting encrypted signal to a plurality of devices with aminimized delay and further an electronic transmission device thereforare presented.

An electronic transmission device of this invention comprises: a firstand second communication means connected to a signal transmission linefor connecting a pair of first and second electronic devices forcommunication; a authentication process means for executing anauthentication process with the first electronic device of a signaltransmitting side through at least the first communication means; adecryption means for decrypting the encrypted signal; and a processmeans for processing the signal obtained by decryption at the decryptionmeans. The authentication process means supplies key information fordecrypting the encrypted signal supplied from the first electronicdevice to the decryption means based on the result of the authenticationprocess and the first communication means supplies the encrypted signalfrom the first electronic device connected by way of the signaltransmission line to the decryption means and the second communicationmeans, and thereby the second communication means is enabled to executethe transmission of the encrypted signal and the key information, and toexecute the authentication process of the second electronic device tothe second electronic device of the signal receiving side.

Further in the signal transmission method, the authentication process isexecuted with the first electronic device of the signal transmittingside connected through the signal transmission line for connecting theelectronic devices, and according to the result of the authenticationprocess, the decryption process is executed for the encrypted signalsupplied from the first electronic device by using key informationsupplied from the first electronic device and thereby the signalprocessing is executed with thus obtained signal. The authenticationprocess or the relay of the authentication process for the secondelectronic transmission device connected through the signal transmissionline is executed and the transmission of the encrypted signal suppliedfrom the first electronic device and the key information for decryptingthe encrypted signal based on a result of the authentication process areexecuted to the second electronic device.

In accordance with the present invention, the authentication process forthe electronic device of the signal transmitting side, the signaltransmission device, for example, connected through the signaltransmission line is executed and if it is judged that the authorizeddevice is connected as a result of the authentication process, then keyinformation is supplied from the signal transmission device. Then theencrypted signal supplied from the signal transmission device isdecrypted with this key information, and an image display operation orthe like of the signal obtained by the decryption is executed. Furtherthe encrypted signal supplied from the signal transmission device issupplied to the electronic device of the signal receiving side, namelythe signal reception device connected through the signal transmissionline, for example. The authentication process or the relay of theauthentication process of this signal reception device with the signaltransmission device, and if it is judged that the authorized device isconnected, then the key information for decrypting the encrypted signalis supplied to the signal reception device.

Further the signal obtained by decrypting the signal from the signaltransmission device is re-encrypted to a encrypted signal different fromthe encrypted signal supplied from the signal transmission device andeither the encrypted signal supplied from the signal transmission deviceor the re-encrypted signal is selected and supplied to the signalreception device. Further when it is judged that the signal receptiondevice is the proper device, then the key information for decrypting thesupplied signal is supplied to the signal reception device.

Further the selection of the encrypted signal supplied from the signaltransmission device or the re-encrypted signal is controlled by either asignal from the signal transmission device or the signal from theoperation input means, and thus selected signal is supplied to thesignal reception device.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a conceptual chart for a signal transmission system of thepresent invention;

FIG. 2 is a chart showing another construction of a signal receptiondevice to be used in the signal transmission system of the presentinvention;

FIG. 3 is a chart showing signal reception devices connected in adaisy-chain connection;

FIG. 4 is a chart for showing a construction of a signal receptiondevice for improving effective legal protection;

FIG. 5 is a chart for showing another construction of a signal receptiondevice for improving effective legal protection;

FIG. 6 is a conceptual chart for a construction of a digital connection;

FIG. 7 is a chart for showing a transmission band of a high-speed serialbus;

FIG. 8 is a chart showing a case where a signal transmission device anda plurality of signal reception devices are connected in a starconnection;

FIG. 9 is a chart showing a case where a signal transmission device anda plurality of signal reception devices are connected in a daisy-chainconnection; and

FIG. 10 is a chart showing a conventional signal reception device havinga relay function.

DETAILED DESCRIPTION

Now, embodiments of the present invention are described in detail withreference to the accompanying drawings as follows. FIG. 1 is aconceptual chart of a signal transmission system for transmitting adigital image signal of contents data, for example. A signaltransmission device 10 (such as a computer apparatus, a set-top box, anoptical disk player or the like) for transmitting the digital imagesignal and a signal reception device 30 (such as a display device, atelevision set or the like) for receiving the digital image signal aremutually connected through a signal transmission line 20 that includesthe TMDS high-speed serial bus that is a transmission line of the DVIformat, a two-way serial bus for information transmission in the DDCformat relating to the Plug & Play proposed by the VESA and/or a signalline for detecting a hot-plug.

In an image signal generating section 11 of the signal transmissiondevice 10 in FIG. 1, three primary color digital image signals DG of thecontents data are generated and supplied to an encryption section 12 byreproducing optical and/or magnetic type recording medium orsemiconductor type recording medium. Or the three primary color digitalimage signals DG are generated based on a data signal for the contentsdata obtained through a communication line and supplied to theencryption section 12. Further in the image signal generating section11, an existence of legal protection for the contents data is judged.For example, necessity of copy protection is judged based on a copyrightprotect information, and then an identification signal PD is supplied toa transmission/reception controlling section 14. As the copyrightprotect information, the CGMS (Copy Generation Management System)information, the CCI (Copy Control Information) information or the likethat designate the contents data to be copy-free, to be copy-inhibitedor to be copy-allowed only once are employed. Further in case oftransmitting a digitized analog image signal by supplying an analogimage signal to the image signal generating section 11, necessity ofcopyright protection may be judged based on the APS (Analog ProtectionSystem) signal used in an analog image signal field. In this case, asignal generation control signal GC is supplied to the image signalgenerating section 11 from the transmission/reception controllingsection 14, and the generation of the three primary color digital imagesignals DG for the contents data is executed with an appropriateresolution and colors suitable for the signal reception device 30.

When the transmission/reception controlling section 14 judges that thethree primary color digital image signals DG to be supplied to theencryption section 12 are legally protected signal based on theidentification signal PD supplied from the image signal generatingsection 11, key information K is supplied to the encryption section 12.

The encryption section 12 executes an encryption of the three primarycolor digital image signals DG by applying the key information Ksupplied from the transmission/reception controlling section 14,generates digital signals DGs of respective color and supplies them tothe transmitting section 13.

The transmitting section 13 executes conversion of the supplied digitalsignal DGs into a base band serial transmission signal SD that issuitable for transmission by encoding process while seeking equalizingof a DC level and minimizing the alternation number of logic levels. Theserial transmission signal SD of respective digital color signals DGS issupplied to the high-speed serial bus through the connector 15.Incidentally, horizontal synchronizing signals and verticalsynchronization signals of the three primary color digital image signalsDG are transmitted by inserting in blanking intervals of the bluedigital image signal, for example.

Further device information such as a model name of a signal receptiondevice is registered at the transmission/reception controlling section14, wherein the signal reception device is to be connected to the signaltransmission device 10. The registered device information designates asignal reception device that does not have a function to copy thecontents data without deteriorating image quality, namely a signalreception device that does not have function to output the supplieddigital image signal and also does not have function to output thedigital image signal by converting into a video signal of the NTSC(National Television Systems Committee) format.

The transmission/reception controlling section 14 executes acommunication with the signal reception device 30-0 through theconnector 15 and the signal transmission line 20-0 in accordance withthe DDC protocol and judges by an authentication process based on thedevice information supplied from the signal reception device 30-0 if theconnected signal reception device 30-0 is registered at thetransmission/reception controlling section 14 as an authorized device,namely a device having no function to copy the contents data withoutdeterioration of the image quality. When the signal reception device30-0 is authenticated as a registered the authorized device, then thekey information to be used upon decrypting the encrypted digital signalDGs is supplied to the signal reception device 30-0. Further thetransmission/reception controlling section 14 controls the generationand the transmission process of the base band serial transmission signalSD by generating and supplying the transmission control signal TC to thetransmitting section 13.

A signal receiving section 32-0 and a signal transmitting/receivingsection 33-0 are connected to a connector 31-0 of the signal receptiondevice 30-0 as a first communication means, and the signal receivingsection 32-0 executes a decrypting process for the received serialtransmission signal SD, generates the three primary color digital signalDGs, and supplies to a decrypting section 51-0 and a transmittingsection 42-0 constructing a second communication means. Further a signaltransmitting/receiving section 33-0 is connected to a signaltransmitting/receiving section 43-0 that constructs a secondcommunication means within the signal reception device and anauthentication process section 50-0 is connected to an internal two-wayserial bus of the signal reception device 30-0.

The authentication process section 50-0 executes an authenticationprocess to the signal transmission device 10 of an electronic device atthe signal transmitting side. Namely, information designating a type ofan electronic device of the signal reception device 30-0 is supplied tothe signal transmission device 10 and the signal transmission device 10judges as if the connected electronic device is an authorized devicebased on the supplied information. When it is judged that the authorizeddevice is connected and the key information Ka for decrypting thedigital signal DGs is then supplied from the signal transmission device10 to the signal reception device 30-0 through the two-way serial bus,after that the authentication process section 50-0 supplies the keyinformation Ka to the decrypting section 51-0.

The decrypting section 51-0 executes decrypting process of the encrypteddigital signal DGs supplied from the signal receiving section 32-0 basedon the key information Ka supplied from the authentication processsection 50-0. The three primary color digital image signals DG obtainedat the decrypting section 51-0 by decryption is supplied to a displaysection 52-0 as a processing means for an image display operation, andthe display section 52-0 executes the image display based on thesupplied three primary color digital image signals DG.

A transmitting section 42-0 executes an encoding process fortransmitting the supplied digital signal DGs similar to the transmittingsection 13, generates a serial transmission signal SD and supplies it toa connector 41-0.

A connector 31-1 of another signal reception device 30-1 is connected tothe connector 41-0 of the signal reception device 30-0 through thesignal transmission line 20-1 constructed by the high-speed serial busor the two-way serial bus. The signal reception device 30-1 has aconstruction similar to the signal reception device 30-0 and theauthentication process section 50-1 of the signal reception device 30-1executes the authentication with the signal transmission device 10 byway of the two-way serial bus like the signal reception device 30-0. Inthis case, when it is judged that the authorized device is connected andthe key information from the signal transmission device 10 is suppliedto the authentication process section 50-1 of the signal receptiondevice 30-1, then the key information Ka is supplied to the decryptingsection 51-1.

The serial transmission signal SD from the transmitting section 42-0 ofsignal reception device 30-0 is supplied to the signal receiving section32-1 of the signal reception device 30-1, and the signal receivingsection 32-1 executes a decrypting process for the serial transmissionsignal SD, generates the digital signal DGs and supplies it to thedecrypting section 51-1 and the transmitting section 42-1, respectively.

The decrypting section 51-1 executes a decryption for the encrypteddigital signal DGs supplied from the signal receiving section 32-1 usingthe key information Ka supplied from the authentication process section50-1, and thus obtained three primary color digital image signals DG aresupplied to the display section 52-1 for image display.

In this case, the serial transmission signal SD supplied to the signalreception device 30-1 is the one that is supplied through the signalreceiving section 32-0 and the transmitting section 42-0 of the signalreception device 30-0 and is not a signal generated after encryption anddecryption. Accordingly, a delay time of the serial transmission signalSD at the signal reception device 30-0 becomes less than the case wherethe serial transmission signal SD is generated after encryption anddecryption, and therefore, timings for displaying the image on thedisplay section 52-0 of the signal reception device 30-0 and fordisplaying the image on the display section 52-1 of the signal receptiondevice 30-1 can be approximately the same time.

Further the signal reception device 30-0 is connected to the signalreception device 30-1, the signal reception device 30-0 becomes anelectronic device of the signal transmitting side, the signal receptiondevice 30-0 connected to the connector 41-1 of the signal receptiondevice 30-1 becomes an electronic device of the signal receiving sideand the signal reception device 30-1 executes a processing similar tothe processing done by the above-mentioned signal reception device 30-0.Similarly, as the supplied signal is transmitted to an electronic deviceof a next stage without decryption or encryption at respective signalreception device, provided that a plurality of signal reception devicesare connected to the signal transmission device 10 in a daisy-chainconnection, a delay time of the serial transmission signal SD becomessmaller than the case where the serial transmission signal is generatedby decryption and encryption and is output, so that a timing of theimage signal of the signal reception device connected to the signaltransmission device can be accorded with a timing of the image of thesignal reception device positioned at end of the signal reception deviceconnected in a daisy-chain connection.

Incidentally, according to the above-mentioned embodiment, anauthentication process is executed among the daisy-chain connectedsignal transmission device and the respective signal reception devicethrough the two-way serial bus, and if it is judged that the authorizeddevice is connected, the key information is transmitted from the signaltransmission device to the signal reception device through the two-wayserial bus, but a load of the authentication process by the signaltransmission device can be reduced by conducting the authenticationprocess among daisy-chain connected signal reception devices.

FIG. 2 shows a construction of the signal reception device 30 a in thecase of conducting the authentication process among the connected signalreception devices. In this case, the signal transmitting/receivingsection 33 and the authentication process section 50 a are connected toeach other and the signal transmitting/receiving section 43 is connectedto the authentication process section 50 a, but the signaltransmitting/receiving section 33 and the signal transmitting/receivingsection 43 are not connected through the internal bus. In this case, anyportions in FIG. 2 corresponding to the portions in FIG. 1 are numberedwith the same reference numerals, and detailed description is omittedhere.

In the authentication process section 50 a, the device informationdesignating a type of the signal reception device is supplied to thesignal transmission device 10 of the signal transmitting side connectedto the connector 31 and executes an authentication with the signaltransmission device 10. Further, like the transmission/receptioncontrolling section 14 of the signal transmission device 10, theauthentication process section 50 a registers the device informationdesignating the signal reception device that does not have a function tocopy the contents data without deterioration of the image quality, andthe authentication process is executed if the authorized device isconnected by comparing the device information supplied from the signalreception device connected to the connector 41 as the signal receivingside with the registered device information.

When it is judged by the authentication with the signal transmissiondevice 10 that the authorized device is connected, and the keyinformation Ka is supplied from the signal transmission device 10, thiskey information Ka is supplied to the decrypting section 51 from theauthentication process section 50 a. Further when it is judged by theauthentication between the authentication process section 50 a and thedevice connected to the connector 41 that the authorized device isconnected, the key information Ka supplied from the signal transmissiondevice 10 is transmitted to the electronic device connected to theconnector 41.

As above-described, when the authentication process is done amongelectronic devices connected in a daisy-chain connection, it is possibleto display images at each signal reception device with approximatelyequal timing to each other and further a load for the authenticationprocess in the signal transmission device can be reduced.

Further in the above-described embodiment, the daisy-chain connectedsignal reception device is the device for the image display andsimultaneous display of the image is done by the plural signal receptiondevices, but these are not limited to the daisy-chain connected deviceshaving image display function. For example, there is a case where afirst copy is legally allowed by the CGMS information, and when thecontents data is copied once, a device having signal recording functionto record the digital signal of the contents data is connected. In thiscase, even the serial transmission signal SD is delayed, the contentsdata can be recorded correctly, so that secure legal protection becomesmore important than the simultaneity of the serial transmission signalSD. Thereby, a signal reception device that can improve the effect ofthe legal protection is shown in FIG. 4 as a third embodiment of thepresent invention. In this case, portions corresponding to portions inFIG. 2 are numbered with the same numerals in FIG. 4 and detailedexplanations are omitted.

The signal transmission device 10 has a function of a display prioritymode that gives a priority to simultaneous display of the image and afunction of a protection priority mode that gives a priority to thehigher legal protection. When it is judged that the authorized device isconnected in the function of the display priority mode, key informationfor decrypting the signal from the transmitting section 13 is suppliedto the signal reception device 30 b as described above. When thefunction is set to the protection priority mode, not only the above keyinformation Ka but also a new key information Kp are together suppliedto the authentication process section 50 b.

The digital signal DGs obtained by conducting the decryption process forthe serial transmission signal SD at the signal receiving section 32 ofthe signal reception device 30 b is supplied to a terminal a of a signalswitching section 58 which constitutes a second communication meanstogether with a decrypting section 51. A terminal b of this signalswitching section 58 is connected to a later described encryptionsection 55 and is supplied with an encrypted digital signal DGu and amoving terminal c is connected to the transmitting section 42. Further amoving terminal c of the signal switching section 58 is switched toeither the terminal a or the terminal b based on the selection signal CSfrom the authentication process section 50 b.

The decrypting section 51 executes the decryption of the supplieddigital signal DGs and thus obtained digital image signal DG is suppliedto the display section 52 and the encryption section 55. In this casewhen the signal reception device 30 b has a signal recording function, asignal recording section is employed instead of the display section 52as a processing means for signal recording operation, and the recordingprocess for the digital image signal DG is executed by this signalrecording section.

The transmitting section 42 b executes the encryption process of thedigital signal DGs or the digital signal DGu selected by the signalswitching section 58 and transmitted through the connector 41 afterconverting into a base-band serial transmission signal SDb that issuitable for transmission.

The authentication process section 50 b supplies the supplied keyinformation Ka to the decrypting section 51, and further when new keyinformation Kp is supplied, the authentication process section 50 bsupplies this key information Kp to the encrypting section 55. Theencrypting section 55 executes the re-encryption of the digital imagesignal DG by applying the key information Kp and generates the digitalencrypted signal DGu and then supplies this to the terminal b of thesignal switching section 58.

Further the authentication process section 50 b generates the selectionsignal CS and supplies to the signal switching section 58 to set themoving terminal c to the terminal a or to set the moving terminal c tothe terminal b when new key information Kp is supplied. Further theauthentication process section 50 b executes the authentication processto the device connected to the connector 41, and if it is judged thatthe authorized device is connected, then, key information for decryptingthe digital signal DGu encrypted by the new key information Kp istransmitted to the device connected to the connector 41. In this case,new key information to be applied at each signal reception device forencrypting process and key information for decrypting the encrypteddigital signal are may be transmitted to each signal reception devicefrom the signal transmission device 10 or may be generated at eachsignal reception device and transmitted to electronic devices connectedthereto. Further a signal switching operation of the signal switchingsection 58 may be directly controlled by the signal transmission device10 through the two-way serial bus depending on the operating mode.

Further when the information designating the electronic device connectedthereto by relaying each signal reception device is reported to thesignal transmission device 10 upon executing the authentication amongelectronic devices, the function at the signal transmission device 10can be automatically switched to either the display priority mode or thelegal protect priority mode depending on the electronic device connectedthereto. For example, any of the signal reception device connected tothe signal transmission device 10 in the daisy-chain connection is theelectronic device that executes only the display operation, then thedisplay priority mode is set, and the electronic device capable ofrecording signal is connected, then automatically switched to the legalprotect priority mode. As described above, when the mode isautomatically switched either the display priority mode or the legalprotect mode depending on the connected device, the mode is set to thedisplay priority mode provided that the all of the signal receptiondevices execute only the display operations, then the encrypted signalencrypted in the signal transmission device 10 is directly and seriallytransmitted between the devices, and accordingly, as described above,the time delay is reduced and the timings of the image display at eachof the signal reception devices can be made the same. Further when thedevice capable of recording signal is connected, the legal protectionpriority mode is selected and the serial transmission signal transmittedamong the electronic devices become one that is based on the digitalsignal encrypted with different key information, and therefore itbecomes difficult to easily obtain the digital image signal and theeffect of the legal protection can be improved accordingly.

Incidentally in the embodiment in FIG. 4, when the new key informationKp is supplied, the signal switching section 58 is arranged to beautomatically controlled by the selection signal CS to output theencrypted signal encrypted based on the new key information Kp. But likethe signal reception device 30 c as shown in FIG. 5, the switchingoperation of the switching section 58 may be controlled based on theoperation signal SE from the operation input section 59. In this case,it becomes possible for a user to arbitrary select an output digitalsignal.

Further although not illustrated, when it is informed that which of thedigital signal is selected to the signal transmission device 10 bysupplying the operation signal SE to the authentication process section50, then the signal transmission device 10 can automatically switch theoperation mode to either the display priority mode or the protectionpriority mode based on the operation of the operation input section 59at the signal reception device.

As described above, even when plural electronic devices are connectedthrough a signal transmission line in a daisy-chain connection, a delayat each device is minimized according to the embodiment of the presentinvention, so that simultaneity of the display image at each electronicdevice can be guaranteed upon connecting the plural electronic devices.Further it is possible to encrypt the transmission signal and totransmit between respective electronic devices with different keyinformation, so that the effect of the legal protection is improved whentransmitting digital signal with a legal protection such as copyrightprotection. Further by connecting a plurality of the electronic devicesin the daisy-chain connection, the number of connectors at each deviceis reduced.

According to the present invention, an authentication process isexecuted with an electronic device of a signal transmission sideconnected through a signal transmission line for connecting betweenelectronic devices, and a decryption is executed for the encryptedsignal supplied from the electronic device of the signal transmittingside. And further the encrypted signal supplied from the electronicdevice of the signal transmitting side is supplied to the electronicdevice of the signal receiving side connected through the signaltransmission line. Further an authentication process or a relay for theauthentication process is executed to the electronic device of thesignal receiving side, and if it is judged that the authorized device isconnected, then key information for decrypting the encrypted signal issupplied to the electronic device of the signal receiving side.

Because of this, even when plural electronic devices are connected inmulti-stage through the signal transmission line for connecting amongdevices, sequentially transmitting signals are not re-encrypted afterdecryption, it is possible to reduce a delay time and if the imagedisplay is executed at each electronic device based on the suppliedsignal, then, the simultaneity of the display image can be maintained.

Further the signal obtained by decrypting the supplied signal from theelectronic device of the signal transmitting side is re-encrypted to thesignal different from the signal supplied from the signal transmissiondevice, and either one of the re-encrypted signal or the encryptedsignal supplied from the electronic device of the signal transmittingside is supplied to the electronic device of the signal receiving side.Further when it is judged that the connected electronic device of thesignal receiving side is the authorized device, then key information fordecrypting the supplied signal is then supplied to the electronic deviceof the signal receiving side.

Accordingly, if the transmission signal is a signal of the contents datato be legally protected, it is possible for the transmission signal tobe an encrypted signal encrypted by different key information betweenelectronic devices, so that an effect of the legal protection can begreatly improved.

1. An electronic transmission apparatus, comprising: first communicationmeans, connected to a signal transmission line, for receiving a firstencrypted signal from a transmitting electronic device over the signaltransmission line; first authentication process means for executing afirst authentication process by which the transmitting electronic deviceauthenticates said first electronic transmission apparatus via saidfirst communication means and the signal transmission line, and forreceiving first key information and second key information from thetransmitting electronic device via said first communication means andthe signal transmission line after the transmitting electronic devicedetermining that said first electronic transmission apparatus is anauthorized device; first decryption means for decrypting the firstencrypted signal using the first key information to obtain a firstdecrypted signal, the first key information being supplied by said firstauthentication process means; first processing means for processing thefirst decrypted signal, said first processing means including a firstsection operable to at least one of display or record the firstdecrypted signal; first encryption means for re-encrypting the firstdecrypted signal using the second key information, the second keyinformation being supplied by said first authentication process means;first signal switching means for receiving a first selection signalprovided by said first authentication process means and which indicateswhether a display priority mode or a legal protect priority mode is set,the first selection signal indicating that the display priority mode isset if a further electronic transmission apparatus does not have arecording capability, and the first selection signal indicating that thelegal protect priority mode is set if the further electronictransmission apparatus has the recording capability, said first signalswitching means selecting the first encrypted signal for output to thefurther electronic transmission apparatus if the display priority modeis set and selecting the first re-encrypted signal for output to thefurther electronic transmission apparatus if the legal protect prioritymode is set, the first encrypted signal being supplied to said firstsignal switching means by said first communication means, the firstre-encrypted signal being supplied to said first signal switching meansby said first encryption means, and second communication means,connected to the signal transmission line, for transmitting the selectedone of the first encrypted signal and the first re-encrypted signal overthe signal transmission line to the further electronic transmissionapparatus if a second authentication process determines that the furtherelectronic transmission apparatus is an authorized device.
 2. Theelectronic transmission apparatus according to claim 1, furthercomprising: second authentication process means for executing the secondauthentication process via the second communication means and the signaltransmission line.
 3. The electronic transmission apparatus according toclaim 1, wherein the first selection signal is supplied by thetransmitting electronic device via said first communication means andthe signal transmission line.
 4. The electronic transmission apparatusaccording to claim 1, further comprising: operation input means forproviding a user-inputted signal for controlling the switching operationof said first signal switching means.
 5. In an electronic transmissionapparatus, a signal transmission method, comprising: executing a firstauthentication process with a transmitting electronic device over asignal transmission line; receiving a first encrypted signal from thetransmitting electronic device over the signal transmission line;receiving first key information and second key information from thetransmitting electronic device over the signal transmission line afterthe transmitting electronic device determines that the first electronictransmission apparatus is an authorized device based on the firstauthentication process; decrypting the first encrypted signal using thefirst key information; at least one of displaying or recording the firstdecrypted signal; re-encrypting the first decrypted signal using thesecond key information; setting a display priority mode if the furtherelectronic transmission apparatus does not have a recording capabilityand setting a legal protect priority mode if the further electronictransmission apparatus has the recording capability; selecting, fortransmission to the further electronic transmission apparatus, the firstencrypted signal if the display priority mode is set or the firstre-encrypted signal if the legal protect priority mode is set; executinga second authentication process between a further electronictransmission apparatus and the electronic transmission apparatus overthe signal transmission line; and transmitting, to the furtherelectronic transmission apparatus, the selected one of the firstencrypted signal and the first re-encrypted signal if it is determinedusing the second authentication process that the further electronictransmission apparatus is an authorized device.
 6. The method accordingto claim 5, wherein said step of executing the second authenticationprocess is carried out between the further electronic transmissionapparatus and the transmitting electronic device in place of theelectronic transmission apparatus.
 7. The method according to claim 5,wherein said step of selecting one of the first encrypted signal and thefirst re-encrypted signal is executed based on a signal received fromthe transmitting electronic device via the signal transmission line. 8.The signal transmission method according to claim 5, wherein said stepof selecting one of the first encrypted signal and the firstre-encrypted signal is executed based on a user-inputted signal.